The present invention relates to image sensors and, more particularly, to image sensors and color filter arrays for charge summing readout modes and interlaced readout modes.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Image sensors may sometimes be referred to herein as imagers. Imagers may be formed from a two-dimensional array of pixels. Each pixel can be configured to receive incident photons (light) and to convert the incident photons into electrical signals.
Many common imagers use the well known Bayer color filter array (CFA) pattern as this pattern provides a known balance between relatively dense color sampling and a layout that helps to minimize aliasing artifacts. Although the Bayer pattern has many benefits, there are several scenarios in which the Bayer pattern performs poorly. Two examples of operational modes in which the Bayer pattern exhibits poor performance are in-pixel charge summing (binning) modes and interlaced readout modes.
In-pixel charge summing readout modes may be used to improve the signal-to-noise ratio of an image produced by an imager. In an in-pixel charge summing readout mode, photoelectric charges from two pixels may be summed together prior to a readout operation. In order to preserve color sampling output, it may be desirable to only perform in-pixel charge summing for pixels that receive light of the same color. However, summing like-colored pixels in this way can be difficult using the Bayer pattern. For example, since red (R) and blue (B) pixels in the Bayer pattern do not have adjacent neighbors of the same color, creating circuits to sum the charges for red and blue pixels in an imager that uses the Bayer pattern is difficult and requires tradeoffs in performance.
Interlaced readout modes in an imager that uses the Bayer color filter array pattern require two fields to be read out from alternating odd and even row pairs to ensure that both fields contain samples of all three color of the Bayer pattern. Since each field skips two rows (i.e., a row pair), using this type of interlaced readout mode in an imager results in undesirable aliasing artifacts and reduces the resolution of any images produced by the imager.
It would therefore be desirable to provide image sensors and color filter arrays for in-pixel charge summing readout modes and for interlaced readout modes.